Barnbird i though i already mentioned I saw the flat spots on the axle tubes on both sides right under the frame rail bump stops?

I have not found the big N yet on the top of the housing but then its kind of hard for me to get my head in there.

I did some research and found the identical posi chuck on the GTO forum i was trying to find pictures of four pinion chucks.

From what i read the four pinion is the heavy duty version you mentioned and should have the side gears in there as well.

My eyes are not great so looking at large pictures helps me.